fix(engine): dispose completed spawned child sessions

.changeset/dispose-spawned-child-sessions.md

@@ -0,0 +1,5 @@
+---
+"@runfusion/fusion": patch
+---
+
+Dispose completed spawned child agent sessions so execution memory is released promptly after `fn_spawn_agent` children finish.

packages/engine/src/__tests__/executor-pause.test.ts

@@ -709,7 +709,8 @@ describe("Agent Spawning - runSpawnedChild", () => {
     // Should transition: running → active
     expect(agentStore.updateAgentState).toHaveBeenCalledWith("agent-test", "running");
     expect(agentStore.updateAgentState).toHaveBeenCalledWith("agent-test", "active");
-    // Should clean up
+    // Should clean up and release session resources
+    expect(mockSession.dispose).toHaveBeenCalledOnce();
     expect(internals.childSessions.has("agent-test")).toBe(false);
     expect(internals.totalSpawnedCount).toBe(0);
   });
@@ -732,7 +733,8 @@ describe("Agent Spawning - runSpawnedChild", () => {
 
     expect(agentStore.updateAgentState).toHaveBeenCalledWith("agent-test", "running");
     expect(agentStore.updateAgentState).toHaveBeenCalledWith("agent-test", "error");
-    // Should still clean up
+    // Should still clean up and release session resources
+    expect(mockSession.dispose).toHaveBeenCalledOnce();
     expect(internals.childSessions.has("agent-test")).toBe(false);
     expect(internals.totalSpawnedCount).toBe(0);
   });
@@ -751,6 +753,7 @@ describe("Agent Spawning - runSpawnedChild", () => {
     // Should not throw even when state updates fail
     await internals.runSpawnedChild("agent-test", mockSession, "Do the research");
 
+    expect(mockSession.dispose).toHaveBeenCalledOnce();
     expect(internals.childSessions.has("agent-test")).toBe(false);
     expect(internals.totalSpawnedCount).toBe(0);
   });

packages/engine/src/executor.ts

@@ -15607,7 +15607,18 @@ You have access to the file system to review changes.${verdictBlock}`;
       const errorMessage = err instanceof Error ? err.message : String(err);
       executorLog.warn(`Child agent ${agentId} failed: ${errorMessage}`);
     } finally {
-      this.childSessions.delete(agentId);
+      /*
+      FNXC:AgentSpawning 2026-06-23-12:25:
+      Server memory must return to baseline after spawned child execution. A normally completed child session owns provider/runtime state until disposed; deleting it from childSessions first makes later parent cleanup unable to reach it.
+      */
+      if (this.childSessions.get(agentId) === childSession) {
+        try {
+          childSession.dispose();
+        } catch (disposeErr) {
+          executorLog.warn(`Child agent ${agentId} session dispose failed: ${disposeErr instanceof Error ? disposeErr.message : String(disposeErr)}`);
+        }
+        this.childSessions.delete(agentId);
+      }
       this.totalSpawnedCount = Math.max(0, this.totalSpawnedCount - 1);
     }
   }